Communication apparatus, method for controlling the same, and non-transitory computer-readable storage medium

ABSTRACT

A communication apparatus that includes a transceiver capable of communicating with the first another communication apparatus operable in accordance with information of a schedule for causing another communication apparatus to operate in a communicable state and the second another communication apparatus inoperable in accordance with the information on the schedule is provided, the information being contained in a first radio signal transmitted by the communication apparatus. The communication apparatus controls, by the schedule, the transceiver so as to transmit the second radio signal for limiting transmission of a radio signal by the second other communication apparatus in at least a part of a period in which the first other communication apparatus operates in a communicable state in a case where the first radio signal is transmitted.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/956,110, filed on Apr. 18, 2018, which claims the benefit of andpriority to Japanese Patent Application No. 2017-085613, filed Apr. 24,2017, each of which is hereby incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to interference suppression control inwireless communication.

Description of the Related Art

In order to save power of a terminal apparatus in a wireless LAN, atechnique of holding a terminal apparatus that need not transmit/receivea signal in a sleep state as much as possible has been examined.Japanese Patent Laid-Open No. 2006-025181 has described a technique of,when an access point searches for an idle timing of a managed wirelesschannel, and then establishes a wireless link with a terminal apparatus,notifying a wireless terminal of the idle timing.

Recently, the IEEE802.11ax standard that aims at using a wireless mediumeffectively is issued as a draft standard. In this standard, a procedurebased on TWT (Target Wake Time) has been proposed in order to save powerof a terminal apparatus. In this procedure, an access point designatestime to activate the terminal apparatus (TWT), and the terminalapparatus is activated in accordance with the notified TWT andtransmits/receives a signal while it is active. This allows the terminalapparatus to shift to a sleep state (Doze state) in a period until theTWT and reduce power consumption. Note that the IEEE802.11ax standardplans to make transmission of individual data signals from the accesspoint to a plurality of terminal apparatuses at the same time ortransmission of signals from the plurality of terminal apparatuses toone access point at the same time, that is, multiuser communicationpossible. Such multiuser communication can be performed by using, forexample, OFDMA that performs multiplexing on a frequency axis or MU-MIMOthat performs multiplexing on a spatial axis.

A terminal apparatus of the first type which is compliant with theIEEE802.11ax standard can interpret a signal that designates TWTtransmitted from the access point and operate in accordance with thedesignated TWT. On the other hand, a terminal apparatus of the secondtype which is not compliant with the IEEE802.11ax standard cannotinterpret the signal that designates the TWT transmitted from the accesspoint. As a result, the terminal apparatus of the second type cannotrecognize a timing at which the terminal apparatus of the first type isactivated, and the transmitted signal may interfere with a controlsignal or a data signal when the terminal apparatus of the first typeperforms communication. At this time, for example, if an interferencewith a trigger signal for causing a plurality of terminal apparatuses ofthe first type to transmit predetermined signals at the same timeoccurs, the predetermined signals may not be transmitted. Then, as aresult, for example, retransmission of the trigger signal may occur,making it impossible for the terminal apparatuses to shift to sleepstates.

SUMMARY OF THE INVENTION

The present invention sets an appropriate communicable period inaccordance with the characteristics of a terminal apparatus.

According to one aspect of the present invention, there is provided acommunication apparatus comprising: a transceiver capable ofcommunicating with a first other communication apparatus operable inaccordance with information of a schedule for causing anothercommunication apparatus to operate in a communicable state and a secondother communication apparatus inoperable in accordance with theinformation of the schedule, the information being contained in a firstradio signal transmitted by the communication apparatus; and acontroller configured to, in a case where the first radio signal istransmitted, control, by the schedule, the transceiver so as to transmita second radio signal for limiting transmission of a radio signal by thesecond other communication apparatus in at least a part of a period inwhich the first other communication apparatus is caused to operate in acommunicable state.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram showing an example of the arrangement of awireless communication system;

FIG. 2 is a block diagram showing an example of the hardware arrangementof an access point;

FIG. 3 is a block diagram showing an example of the functionalarrangement of the access point;

FIG. 4 is a timing chart showing the procedure of communication controlbased on TWT (Target Wake Time);

FIG. 5 is a timing chart showing the outline of the sequence of systemprocessing according to processing example 1;

FIG. 6 is a flowchart showing an example of the sequence of access pointprocessing according to processing example 1;

FIG. 7A is a view showing an example of a PSMP (Power Save Multi-Poll)frame;

FIG. 7B is a timing chart showing the procedure of communication controlbased on PSMP (Power Save Multi-Poll);

FIG. 8 is a timing chart showing the outline of the sequence of systemprocessing according to processing example 2;

FIG. 9 is a flowchart showing an example of the sequence of access pointprocessing according to processing example 2;

FIG. 10 is a timing chart showing the outline of the sequence of systemprocessing according to processing example 3; and

FIG. 11 is a flowchart showing an example of the sequence of accesspoint processing according to processing example 3.

DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment(s) of the present invention will now bedescribed in detail with reference to the drawings. It should be notedthat the relative arrangement of the components, the numericalexpressions and numerical values set forth in these embodiments do notlimit the scope of the present invention unless it is specificallystated otherwise.

(System Arrangement)

FIG. 1 shows an example of a wireless communication system according tothis embodiment. This wireless communication system includes an accesspoint (AP) 101 and wireless terminals 102 to 104. Note that the AP 101and the wireless terminals 102 to 104 are wireless communicationapparatuses complying with one of the IEEE802.11 standards. However, thewireless terminal 104 does not comply with the IEEE802.11ax standard,and the other apparatuses comply with the IEEE802.11ax standard. Notethat the AP 101 can be connected to the Internet 105 or the like by, forexample, wired connection.

In this embodiment, the AP 101 can perform power-saving processing basedon TWT (Target Wake Time) with the plurality of wireless terminals 102and 103 operable in accordance with the IEEE802.11ax standard. Thisprocessing will be described later. Then, the AP 101 performs processingwhich is not interfered by the wireless terminal 104 that does notcomply with the IEEE802.11ax standard on communication related to thisprocessing based on this TWT. In an example, the AP 101 controlscommunication of the wireless terminal 104 such that the communicationof the wireless terminal 104 is performed while the wireless terminals102 and 103 are in sleep (Doze) states.

For this purpose, for example, the AP 101 sends a CTS (Clear ToSend)-to-self frame so the wireless terminal 104 does not transmit asignal in a period during which communication with the wirelessterminals 102 and 103 is performed. Note that a NAV (Network AllocationVector) designated by the CTS-to-self frame is set to be in a perioduntil at least the completion of a period in which multiusercommunication between the wireless terminals 102 and 103 and the AP 101is performed. Accordingly, the wireless terminal 104 does not transmit asignal in the period in which multiuser communication between thewireless terminals 102 and 103 and the AP 101 is performed, andtransmits a signal after the wireless terminals 102 and 103 are set inthe Doze states. This allows the AP 101 to reduce a probability that asignal from a wireless terminal which is not compliant with theIEEE802.11ax standard interferes with a signal according to theIEEE802.11ax standard.

The AP 101 can also control communication of the wireless terminal 104by using the mechanism of PSMP (Power Save Multi Poll). The AP 101 candesignate, by a PSMP frame, a period in which communication between anuplink and a downlink should be performed with the wireless terminal104. The wireless terminal 104 can perform communication in a perioddesignated by the PSMP frame and be set in the Doze state in theremaining period. The AP 101 can prevent a signal transmitted by thewireless terminal 104 from interfering with multiuser communication withthe wireless terminals 102 and 103 by, for example, forming the PSMPframe so as to perform communication in a period different from theperiod in which the multiuser communication is performed.

Furthermore, the AP 101 can set a CFP (Contention Free Period) forcontrolling the right of access to the medium of each wireless terminal.The CFP is a period in which only a wireless terminal that has receivedpolling from the AP 101 obtains the right to access to the medium. Byusing this, the AP 101 sets, as the CFP, the period different from theperiod in which multiuser communication is performed with the wirelessterminals 102 and 103, and communicates with the wireless terminal 104.This allows the AP 101 to cause the wireless terminal 104 to communicatewhile the wireless terminals 102 and 103 are in the Doze states, andprevent the signal transmitted by the wireless terminal 104 frominterfering with multiuser communication.

In the following description, the arrangement of the AP 101 thatperforms such processing will be described first, communication controlbased on TWT and communication control based on PMSP to be used in anexplanation below will briefly be described next, and then an example ofprocessing performed by the AP 101 will be described. Note that each ofthe wireless terminals 102 and 103 is a general wireless LAN terminalhaving a communication function complying with the IEEE802.11axstandard, and thus its arrangement will not be described in detail here.The wireless terminal 104 is also a general wireless LAN terminal havinga communication function complying with, for example, one of theIEEE802.11 standards different from the IEEE802.11ax, and thus itsarrangement will not be described in detail here. However, the wirelessterminal 104 cannot interpret at least some control signals such as atrigger signal according to the IEEE802.11ax standard. Note that awireless LAN terminal will sometimes be referred to as an “STA”hereinafter. A description will be given below assuming that theIEEE802.11ax standard is used. However, the present invention is notlimited to this. That is, the same processing can be performed in a casein which the first terminal apparatus complying with a predeterminedstandard and the second terminal apparatus complying with a succeedingstandard of the predetermined standard coexist, and the first terminalapparatus cannot interpret a control signal according to the succeedingstandard. A predetermined function and signal will be described below byusing technical terms regarding the IEEE802.11 standards. However, atechnique according to this embodiment should be understood by replacingthem with another function and signal having the same significance asthe terms.

(Apparatus Arrangement)

FIG. 2 is a block diagram showing an example of the hardware arrangementof the AP 101 according to this embodiment. The AP 101 includes, forexample, a storage unit 201, a controller 202, a functional unit 203, aninput unit 204, an output unit 205, a communication unit 206, and anantenna 207 as its hardware arrangement.

The storage unit 201 is formed by both a ROM and a RAM or one of them,and stores programs for performing various operations to be describedlater, and various kinds of information such as communication parametersfor wireless communication. The ROM stands for a “Read Only Memory”, andthe RAM stands for a “Random Access Memory”. Note that as the storageunit 201, it is also possible to use a storage medium such as a flexibledisk, a hard disk, an optical disk, a magnetooptical disk, a CD-ROM, aCD-R, a magnetic tape, a nonvolatile memory card, or a DVD, instead ofthe memory such as a ROM or RAM. The storage unit 201 may also be formedby a plurality of memories or the like.

The controller 202 is formed by a CPU or a MPU, and controls the wholeAP 101 by executing the programs stored in the storage unit 201. The CPUstands for a “Central Processing Unit”, and the MPU stands for a “MicroProcessing Unit”. Note that the controller 202 may also control thewhole AP 101 in cooperation with the programs and an OS stored in thestorage unit 201. The OS stands for an “Operating System”. Note alsothat the controller 202 may be formed by a plurality of processors suchas multicores. As the controller 202, it is also possible to use an FPGA(Field Programmable Gate Array), a DSP (Digital Signal Processor), anASIC (Application Specific Integrated Circuit), or the like. Thecontroller 202 executes predetermined processes such as an access pointfunction, image capturing, printing, and image projection by controllingthe functional unit 203.

The functional unit 203 is hardware which allows the AP 101 to executethe predetermined processes. For example, if the AP 101 is a camerahaving an access point function, the functional unit 203 is an imagecapturing unit for performing an image capturing process. Alternatively,for example, if the AP 101 is a printer having an access point function,the functional unit 203 is a printing unit for performing printprocessing. Alternatively, for example, if the AP 101 is a projectorhaving an access point function, the functional unit 203 is an imageprojection unit for performing image projection processing. Data to beprocessed by the functional unit 203 can be data stored in the storageunit 201, and can also be data obtained by communication performed withanother apparatus via the communication unit 206 (to be describedlater).

The input unit 204 accepts various operations from a user. The outputunit 205 performs various outputs to the user. The outputs by the outputunit 205 herein mentioned include at least one of image display on thescreen, sound output by a loudspeaker, vibration output, and the like.Note that it is also possible to implement the input unit 204 and theoutput unit 205 by one module such as a touch panel.

The communication unit 206 performs control of wireless communicationcomplying with the IEEE802.11 series (such as the Wi-Fi standard), andcontrol of IP communication. An IP stands for an “Internet Protocol”.The communication unit 206 transmits and receives radio signals forwireless communication by controlling an antenna 207. The AP 101 cancommunicate contents such as image data, document data, and video datawith a wireless terminal and can also relay communication between thewireless terminals connected to the AP 101 via the communication unit206. Note that the communication unit 206 has, for example a wiredcommunication function and can relay communication between a wirelessterminal and a network such as the Internet by being connected to thenetwork.

FIG. 3 is a block diagram showing an example of the arrangement of theAP 101. The AP 101 includes, for example, a wireless LAN controller 301,an 11ax communication controller 302, and a non-11ax communicationcontroller 303. Note that each function shown in FIG. 3 can beimplemented by, for example, causing the controller 202 of FIG. 2 toexecute the programs stored in the storage unit 201 but may beimplemented by dedicated hardware such as a communication control chip.

The wireless LAN controller 301 controls whole communication processingwhen the AP 101 communicates with a wireless LAN terminal. When thewireless LAN terminal complies with the IEEE802.11ax standard, the 11axcommunication controller 302 performs control such that the wireless LANcontroller 301 performs communication by a procedure defined by theIEEE802.11ax standard. The non-11ax communication controller 303controls communication by the wireless LAN controller 301 when thewireless LAN terminal does not comply with the IEEE802.11ax standard.For example, the non-11ax communication controller 303 performscommunication control so the wireless LAN terminal noncompliant with theIEEE802.11ax does not interfere with the communication controlled by the11ax communication controller 302. An example of each process to bedescribed below is performed by, for example, the non-11ax communicationcontroller 303.

(Communication Control Based on TWT)

An example of the sequence of communication control based on TWT to beadopted by the IEEE802.11ax standard will now be described withreference to FIG. 4 . Note that TWT can be set individually for eachwireless terminal. However, an example in which common TWT is set for aplurality of wireless terminals will be described below.

First, a wireless terminal (STA-A) compliant with the IEEE802.11axstandard transmits a TWT request 401 (TWT req.) in order to request apower-saving schedule from an AP. Then, upon receiving the TWT request401, the AP transmits a TWT response 402 (TWT resp.). Note that a period403 from the TWT request 401 to the TWT response 402 is a section of aTBTT negotiation, and the First TBTT and a Listen Interval aredetermined in this section. Note that a TBTT stands for “Target BeaconTransmission Time”. The First TBTT indicates an interval 404 from theTWT response 402 to the start of a preparation for transmission of aBeacon 407 (notification signal) with a TWT IE (Information Element).The Listen Interval indicates a transmission interval 417 of the Beaconwith the TWT IE. Note that in FIG. 4 , a Beacon 426 does not include theTWT IE, and a Beacon with the TWT IE transmitted after the Beacon 407 isa Beacon 427. In this case, a period from the end of transmission of theBeacon 407 to the start of transmission of the Beacon 427 is set for theListen Interval, and the Beacon 426 is ignored in the setting of theListen Interval. The wireless terminal identifies, by the First TBTT,the timing of, for example, a Beacon with a TWT IE transmitted firstafter receiving the TWT response. Then, the wireless terminal canfurther identify, in accordance with the Listen Interval, thetransmission timing of a Beacon with a TWT IE transmitted periodicallyafterward.

Note that upon receiving the TWT response 402, the STA-A shifts to aDoze state 405 (can also be referred to as a Sleep state or apower-saving state) until a transmission preparation timing of a Beaconwith the first TWT IE designated at the First TBTT. Note that forexample, an STA-B transmits the TWT request to the AP before the processof FIG. 4 is started. Then, the STA-B stays in a Doze state 406 untilthe transmission timing of a Beacon including a next TWT IE that isidentified based on the Listen Interval.

Each of the STA-A and the STA-B shifts from the Doze state to an activestate capable of performing communication at a timing when transmissionof the Beacon 407 with the TWT IE is prepared and waits for the Beacon407. Let t0 be time at which transmission of the Beacon 407 is complete.

In the TWT IE of the Beacon 407, a TWT1 408 of a time intervalimmediately after transmission of the Beacon 407 to the transmissionpreparation of a Trigger frame 413 for the AP to accept polling isdesignated. Let t1 be end time of this TWT1 408. Upon receiving theBeacon 407, the STA-A and the STA-B shift to Doze states 411 and 412,and return to the active states in accordance with the end of the TWT1408. Then, after the end of the TWT1 408, the AP transmits the Triggerframe 413 for causing the STA-A and the STA-B to transmit pollingframes. Upon receiving this Trigger frame 413, the STA-A and the STA-B,respectively, transmit PS-Poll frames 414 and 415 as polling signals inthe power-saving state. Note that the PS-Polls 414 and 415 aretransmitted from the STA-A and the STA-B simultaneously by using theTrigger frame 413 as a trigger. Note that signals from a plurality ofSTAs can be multiplexed and transmitted in a frequency domain or aspatial domain by OFDMA (Orthogonal Frequency-Division Multiple Access)or UL MU-MIMO (UpLink MultiUser MIMO). Upon receiving the pollingsignals from the STA-A and the STA-B, the AP transmits amultistation-block ACK 416 (M-BA) in order to return an acknowledge tothese signals simultaneously. Let t2 be transmission end time of thisM-BA. Note that a period 410 from t0 to t2 is a communication enableperiod based on a trigger (Trigger-enabled TWT SP (Service Period)). TheTrigger-enabled TWT SP is designated by, for example, the TWT IE of theBeacon 407, and the STA-A and the STA-B can maintain the active statesuntil the expiration of this period after the TWT1.

In addition, in the TWT IE of the Beacon 407, a TWT2 409 of a timeinterval immediately after transmission of the Beacon 407 until thetransmission preparation of a downlink multiuser packet (DL MU PPDU 421)is made is also designated. After receiving the M-BA 416, the STA-A andthe STA-B shift to Doze states 418 and 419 again, and return to theactive states at end time t3 of the TWT2 409. Upon completion of thetransmission preparation of the DL MU PPDU 421, the AP transmits packetsto the STA-A and the STA-B. Upon succeeding in receiving this DL MU PPDU421, the STA-A and the STA-B transmit block ACK (BA) to the AP. Theblock ACK can be multiplexed in a frequency domain or a spatial domain,but its contents are the same as block ACK used in a conventionalwireless LAN, and thus a description thereof will be omitted. Note thata period 420 in which this DL MU PPDU 421 is transmitted, and BAs 422and 423 are transmitted is a period unannounced by the TWT IE of theBeacon 407 and is referred to as an Unannounced TWT SP. Note that let t4be end time of the period 420. After the end of the period 420, theSTA-A and the STA-B shift to Doze states 424 and 425 until thetransmission timing (or a preparation start timing of the transmission)of the Beacon 427 with the next TWT IE.

As described above, the plurality of wireless terminals compliant withthe IEEE802.11ax can achieve power saving by conducting a negotiationregarding a TWT with the AP and efficient simultaneous signaltransmission in an uplink direction by Trigger.

Note that a terminal which is not compliant with the IEEE802.11axstandard cannot grasp duration times of these Trigger frame 413,PS-Polls 414 and 415, and M-BA 416 from information elements of theseframes. Thus, an STA-C noncompliant with the IEEE802.11ax may be addedto such a network and transmit a signal that interferes with a Triggerframe.

In order to prevent occurrence of such an interference, the APcommunicates with the wireless terminal (STA-C) which is not compliantwith the IEEE802.11ax while the wireless terminals (STA-A and STA-B)operating in accordance with the IEEE802.11ax standard are in the Dozestates. For this purpose, the AP transmits a predetermined signal so thewireless terminal which is not compliant with the IEEE802.11ax does nottransmit a signal while the wireless terminals operating in accordancewith the IEEE802.11ax standard are not in the Doze states. Such aprocess will be described below by using some examples.

<Processing Example 1>

In this processing example, the AP uses CTS-to-self to cause thewireless terminal (STA-C) which is not compliant with the IEEE802.11axto set a transmission prohibition period (NAV) and prevent occurrence ofan interference with communication of the wireless terminals operatingin accordance with the IEEE802.11ax standard. This processing will bedescribed with reference to FIG. 5 . Note that FIG. 5 is the same asFIG. 4 except that reference numerals are given.

Note that regarding communication from the AP to the STA-C, the APrecognizes the period in which the STA-A and the STA-B are in the Dozestates, and thus can transmit a signal in that period. Note that if theSTA-C receives a radio signal from the AP, it can transmit a response(ACK) to it. Therefore, for example, if the length of a period from thetime t0 to the time t1 in which the STA-A and the STA-B are in the Dozestates is a sufficient length for performing transmission of a downlinksignal and response reception, the AP can determine to transmit thedownlink signal. Note that the AP may determine or transmit the downlinksignal as described above in accordance with, for example, accumulationof data to be transmitted to the STA-C in a buffer. Note that FIG. 5shows an example in which the AP transmits a downlink signal 505 to theSTA-C in a period from time t4 to time t5 out of the period in which theSTA-A and the STA-B are in the Doze states. Note that the time t5indicates transmission start time of the Beacon 427 with the next TWTIE.

In order to prevent the STA-C from transmitting an uplink signal duringcommunication with the STA-A and the STA-B, the AP transmits CTS-to-self501 and stops signal transmission by a wireless terminal which exists onthe periphery and does not operate based on TWT. Note that let t6 betransmission end time of this CTS-to-self 501. At this time, because theSTA-A and the STA-B shift to the Doze states at the time t2, the AP canset the length of a transmission prohibition section as t2-t6 so as toset a period until the time t2 to be a NAV period 502 a. Because theSTA-A and the STA-B shift to the Doze states at the time t4, the AP canset the length of a transmission prohibition section as t4-t6 so as toset a period until the time t4 to be a NAV period 502 b. Note that theAP can determine the times t1 to t5 when transmitting the Beacon 407with the TWT IE, and thus can determine t2-t6 and t4-t6 of the lengthsof the transmission prohibition sections appropriately. When the NAVperiod 502 a is set, the STA-C transmits an uplink signal 503 to the APin a period from the time t2 to the time t3 in which the STA-A and theSTA-B are in the Doze states. On the other hand, when the NAV period 502b is set, the STA-C transmits an uplink signal 504 to the AP in a periodfrom the time t4 to the time t5 in which the STA-A and the STA-B are inthe Doze states. Note that upon receiving these uplink signals, the APtransmits a response signal (ACK) to the STA-C.

Note that the STA-A and the STA-B shift to the Doze states in the periodof TWT1 (from the time t0 to the time t1), and thus do not update theNAV by CTS-to-self. Even if CTS-to-self is received, the STA-A and theSTA-B can perform the subsequent transmission operation of an uplinksignal by receiving the Trigger frame 413.

FIG. 6 shows a process performed by the AP concerning the uplink of theSTA-C. Note that FIG. 6 omits matters other than the communication ofthe STA-C such as communication with the STA-A and the STA-B for thesake of descriptive simplicity. The AP can transmit a downlink signalwhile the STA-A and the STA-B are in the Doze states, as describedabove.

In this process, the AP first determines whether the length of a periodbetween the time t2 and the time t3 in which the STA-A and the STA-Bshift to the Doze states is sufficient to perform uplink communicationfrom the times t1 to t5 determined when the Beacon 407 with the TWT IEis generated. That is, the AP determines whether t3-t2 is equal to orlarger than a predetermined value which is the sum of one transmissionright time (TXOP) of the STA-C and a time required to transmit aresponse signal (ACK) to it in uplink communication (step S601). Notethat this determination can be made, for example, when the Beacon 407 isgenerated or after the Beacon 407 is transmitted. Alternatively, the AP,for example, may first determine whether data to be transmitted to theSTA-C in a downlink exists, transmit such data if the data exists, andthen make the above-described determination. Alternatively, if such dataexists, the AP may transmit such data when it can complete transmissionof downlink data, reception of a response to it, and transmission ofCTS-to-self to be described later between the time t0 and the time t1.

If the AP determines that t3-t2 is equal to or larger than theabove-described predetermined value (YES in step S601), it determinesthat the period from the time t2 to the time t3 is sufficient for theSTA-C to transmit data and determines that the STA-C sets a period untilthe time t2 as a NAV period. In this case, the AP sets a Duration to beincluded in CTS-to-self to t2-t6 by using t6 of the transmissioncompletion time of CTS-to-self (step S602). Then, the AP sendsCTS-to-self that has designated this Duration (step S604). Uponreceiving this CTS-to-self, the STA-C sets the NAV period of the lengthof t2-t6 and does not transmit a signal until the elapsation of thisperiod. As a result, the STA-C transmits an uplink signal after the timet2 at which the NAV period expires (YES in step S605). Upon receivingthis uplink signal (step S606), the AP transmits a response signal (stepS607) and terminates the process. On the other hand, if the APdetermines that t3-t2 is smaller than the above-described predeterminedvalue (NO in step S601), it determines that the period from the time t2to the time t3 is insufficient to transmit the data and determines thatthe STA-C sets a period until the time t4 as a NAV period. That is, theAP determines to grant a data transmission right to the STA-C in theperiod from the time t4 to the time t5 capable of ensuring a relativelylong period for communication after the completion of transmission ofthe DL MU PPDU 421. In this case, the AP sets a Duration to be includedin CTS-to-self to t4-t6 (step S603). The subsequent processes are thesame as in steps S604 to S607 as described above. Consequently, theSTA-C sets a NAV period of the length of t4-t6 upon receiving thisCTS-to-self, does not transmit a signal until the elapsation of theperiod, and transmits an uplink signal after the time t4.

Note that, for example, in the period from the time t4 to the time t5,if downlink data to be transmitted to the STA-C exists, the AP can alsotransmit the data and receive a response to it. The AP can performtransmission of this downlink data or the like, for example, afterreception of an uplink signal from the STA-C and transmission of aresponse to it.

As described above, in this processing example, CTS-to-self that can beinterpreted by any wireless terminal complying with one of theIEEE802.11 standard series is used to control communication. This makesit possible to prevent a wireless terminal incapable of interpreting asignal of a new standard such as the IEEE802.11ax from interfering withcommunication in the new standard.

<Processing Example 2>

In this processing example, the AP uses PSMP (Power Save Multi Poll) tocontrol a timing at which the wireless terminal (STA-C) which is notcompliant with the IEEE802.11ax performs communication.

First, the procedure of the PSMP will be described with reference toFIGS. 7A and 7B. In the PSMP, the AP transmits a PSMP frame for definingcommunication periods of an uplink and a downlink. FIG. 7A shows anexample of a PSMP frame 701. FIG. 7B shows an example of the sequence ofcommunication control using the PSMP frame.

In the PSMP frame 701, an STA_INFO Type 702 is a field indicating theapplication of this PSMP frame 701, that is, whether it is for broadcastor multicast, or it is addressed to an individual wireless terminal. Forexample, “0” if the PSMP frame 701 is for broadcast, “1” if the PSMPframe 701 is for multicast, and “2” if the PSMP frame 701 is addressedto the wireless terminal individually are stored in the STA_INFO Type702. Here, the PSMP frame 701 is addressed to the wireless terminalindividually, and thus a value “2” is stored in the STA_INFO Type 702.

Each of a PSMP-DTT Start Offset 703 and a PSMP-DTT Duration 704 isinformation indicating a period set for downlink signal transmission. Avalue indicating an offset value from time at which transmission of thePSMP frame 701 is complete to time at which downlink transmission isstarted is stored in the PSMP-DTT Start Offset 703. That is, thewireless terminal can determine that reception of a downlink signal isstarted at time when an offset period indicated by the PSMP-DTT StartOffset 703 has elapsed after reception of the PSMP frame 701. A valueindicating the length of a period in which downlink communicationcontinues from time identified by the PSMP-DTT Start Offset 703 isstored in the PSMP-DTT Duration 704. An example in a case in whichdownlink transmission addressed to an STA-D is performed in a periodfrom time t11 to time t12 as shown in FIG. 7B will be described here.Note that reference numeral t10 denotes completion time of a PDMP framehere. In this case, a value “t11-t10” is stored in the PSMP-DTT StartOffset 703 of a time offset until the start of downlink transmission. Onthe other hand, a value “t12-t11” is stored in the PSMP-DTT Duration 704of a time length from the start to end of downlink transmission.

Each of a PSMP-UTT Start Offset 706 and a PMSP-UTT Duration 707 isinformation indicating a period set for uplink signal transmission.These values are set in the same manner as the PSMP-DTT Start Offset 703and the PSMP-DTT Duration 704. That is, a value indicating an offsetvalue from time at which transmission of the PSMP frame 701 is completeto time at which uplink transmission is started is stored in thePSMP-UTT Start Offset 706. A value indicating the length of a period inwhich uplink communication continues from time identified by thePSMP-UTT Start Offset 706 is stored in the PMSP-UTT Duration 707.Therefore, as shown in FIG. 7B, when uplink transmission from the STA-Dis performed in a period from time t13 to time t14, a value “t13-t10” isstored in the PSMP-UTT Start Offset 706. A value “t14-t13” is stored inthe PMSP-UTT Duration 707.

An STA ID 705 stores an AID (Association IDentifier) for identifying awireless terminal of the destination of this PSMP frame 701. Reserved708 is a reservation field.

In FIG. 7B, first, the AP 101 transmits a PSMP frame 711 that defineseach field as described above to each STA. Note that here, with respectto the STA-D, the AP assigns the period from the time t11 to the timet12 to downlink transmission and assigns the period from the time t13 tothe time t14 to uplink transmission, as described above. With respect toan STA-E, the AP sets the value of each field so as to assign a periodthat does not overlap these periods to downlink transmission and uplinktransmission, and transmits the PSMP frame 711.

The AP transmits a downlink signal 712 for the STA-D in an STA-Ddownlink period (from the time t11 to the time t12) designated by thePSMP frame 711. At this time, the STA-E is set in a Doze state 713because the period is not a communication period assigned to itself.Subsequently, the AP transmits a downlink signal for the STA-E 714 in anSTA-E downlink period designated by the PSMP frame 711. In this period,the STA-D is set in a Doze state 715 because the period is not acommunication period assigned to itself.

Subsequently, the STA-D transmits an uplink signal 716 for the AP in anSTA-D uplink period (from the time t13 to the time t14) designated bythe PSMP frame 711. Note that in this period, the STA-E is set in a Dozestate 717 because the period is not a communication period assigned toitself. Subsequently, the STA-E transmits an uplink signal 718 for theAP in an STA-E uplink period designated by the PSMP frame 711. Note thatin this period, the STA-D is set in a Doze state 719 because the periodis not a communication period assigned to itself.

Note that the STA-D can be set in a Doze state, for example, only in aperiod for uplink transmission or downlink transmission assigned to theSTA-E. Similarly, the STA-E can be set in a Doze state only in a periodfor uplink transmission or downlink transmission assigned to the STA-D.

The sequence of a process according to this processing example will nowbe described with reference to FIG. 8 . In this processing example, theAP identifies a communication period with the STA-C by using a PSMPframe. Note that FIG. 8 is the same as FIG. 4 except that referencenumerals are given. The AP determines a period in which downlink anduplink communications are performed with the STA-C, generates a PSMPframe 801 for designating the period, and transmits it to the STA-C.Note that in FIG. 8 , the PSMP frame 801 is transmitted before theBeacon 407 with the TWT IE, but the present invention is not limited tothis. Here, the AP recognizes the times t1 to t5 designated by the TWTIE and the time t0 at which transmission of the Beacon 407 is completeif the PSMP frame 801 is transmitted before the Beacon 407. The AP canselect, for example, one of (a) a period from the time t0 to the timet1, (b) a period from the time t2 to the time t3, and (c) a period fromthe time t4 to the time t5 in which the STA-A and the STA-B are in theDoze states as a period for communication with the STA-C. The APselects, for example, a period longer than a time length required fortransmission of a downlink signal to the STA-C and reception of aresponse, and reception of an uplink signal from the STA-C andtransmission of a response from the above-described periods (a) to (c).Then, in accordance with the selected period, the AP sets one of asetting a to a setting c and sets each field of the PSMP frame 801. InFIG. 8 , settings corresponding to these periods (a) to (c) arerepresented as the settings a to c. In accordance with this setting, theSTA-C receives a downlink signal, transmits a response to it, transmitsan uplink signal, and receives a response to it. For example, if theSTA-C receives the PSMP frame 801 that designates the setting a from theAP, it receives a downlink signal 802 a from the AP and transmits anuplink signal 803 a to the AP 101. Similarly, if the STA-C receives thePSMP frame 801 that designates the setting b (setting c) from the AP, itreceives a downlink signal 802 b (signal 802 c) from the AP andtransmits an uplink signal 803 b (signal 803 c) to the AP. Note that theAP may generate, for example, a PSMP frame indicating that a period inwhich the STA-A and the STA-B perform multiuser communication isassigned to communication to a wireless terminal other than the STA-C,and transmit the PSMP frame to the STA-C. In this case, the STA-C canrecognize that a period in which the STA-A and the STA-B performcommunication is not a period assigned to itself, and thus can shift toa Doze state. As a result, the STA-C does not transmit a signal in theperiod in which the STA-A and the STA-B perform communication, making itpossible to prevent an interference with a signal regarding theIEEE802.11ax.

A process performed by the AP will now be described with reference toFIG. 9 . First, based on the length of a period in which the STA-A andthe STA-B stay in the Doze states, and the length of a period requiredfor communication with the STA-C, the AP sets a period in whichcommunication with the STA-C is performed (step S901). Note that here,the AP selects a setting to be applied, for example, among the setting ato the setting c of FIG. 8 and determines the setting. Subsequently,based on the determined setting and the transmission end timing (time t7in FIG. 8 ) of the PSMP frame, the AP stores a value in each field inthe PSMP frame and transmits it to the STA-C (step S902). Upon reachingthe start time of the set period (step S903), the AP then performs datacommunication in a downlink (steps S904 and S905) and data communicationin an uplink (steps S906 and S907) in the set period.

In this processing example, by using the PSMP, it becomes possible toprevent the signal transmitted from the STA-C from interfering with asignal (for example, the Trigger frame 413) regarding communicationbetween the AP, and the STA-A and the STA-B. For example, when the AP isconnected to a plurality of wireless terminals which are not compliantwith the IEEE802.11ax standard, it can finely control periods ofcommunication in the downlink and communication in the uplink withrespect to these wireless terminals by using a PSMP frame. Note that theAP can confirm whether the STA-C supports the PSMP by exchangingcapability information at the time of connection with the STA-C. Thisallows the AP to use a method of this processing example only if theSTA-C supports the PSMP. Note that if the STA-C does not support thePSMP, the AP can communicate with the STA-C by using, for example, amethod in processing example 1 or a method of processing example 3 to bedescribed later. That is, in accordance with the capability informationof the STA-C, the AP can change the type of signal to be transmitted toset a communicable period of the STA-C appropriately.

<Processing Example 3>

In this processing example, the AP uses a CFP (Contention Free Period)to prevent a signal from the wireless terminal (STA-C) noncompliant withthe IEEE802.11ax from interfering with communication of a wirelessterminal which operates in accordance with the IEEE802.11ax standard.The CFP is a method for controlling medium access by a wireless terminalbeing connected to a control station (in this case, the AP). The APtransmits a polling frame (a CF-Poll or a QoS CF-Poll) to a wirelessterminal that grants an access right to a wireless medium during theCFP. In a CFP period, the wireless terminal can acquire the access rightto the wireless medium only when the polling frame is received andperform signal transmission to the AP. When the CFP is used, the AP canstore a value indicating that the CFP is set and a value indicating theduration time of the CFP, for example, in the Beacon 407 or a searchresponse signal to a search request signal when each wireless terminalsearches for the AP and transmit these values. Note that the APtransmits signals while containing these pieces of information in theBeacon 407 below. Upon receiving these signals, the wireless terminalcan obtain the duration time of the CFP stored in the signals, set theperiod as a NAV period, and monitor a polling frame. This processingwill be described with reference to FIG. 10 . Note that FIG. 10 is thesame as FIG. 4 except that reference numerals are given.

FIG. 10 determines the length of the CFP, for example, beforetransmission of the Beacon 407. For example, the AP determines whetherit is possible to complete communication of the STA-C in the period fromthe time t0 to the time t1 or the period from the time t2 to the timet3. Then, for example, if the AP determines that it is possible tocomplete communication of the STA-C in the period from the time t0 tothe time t1, it determines to perform communication of the STA-C in thatperiod. Similarly, for example, if the AP determines that it is possibleto complete communication of the STA-C in the period from the time t2 tothe time t3, it determines to perform communication of the STA-C in thatperiod. Then, if the AP determines to perform communication of the STA-Cin the period from the time t0 to the time t1, it determines, forexample, the CFP as the period from the time t0 to the time t2. On theother hand, if the AP determines to perform communication of the STA-Cin the period from the time t2 to the time t3, it determines, forexample, the CFP as a period from the time t0 to the time t4. Then, theAP transmits a polling frame 1002 a or 1002 b to the STA-C in a periodin which communication with the STA-C is to be performed, and the STA-Cresponds to this polling frame and transmits an uplink signal 1003 a or1003 b to the AP. Note that the AP may determine, for example, the CFPas the period from the time t0 to the time t4 regardless of whethercommunication of the STA-C is performed in one of the period from thetime t0 to the time t1 and the period from the time t2 to the time t3.According to this, it is possible to cause the STA-C not to transmit asignal in, for example, a period from the time t1 to the time t2 or theperiod from the time t3 to the time t4. Note that FIG. 10 shows anexample in which the STA-C transmits the uplink signal during the CFP.However, the AP may transmit a downlink signal during this period.Alternatively, the AP may transmit the downlink signal in the periodfrom the time t4 to the time t5.

The sequence of a process by the AP in this processing example will nowbe described with reference to FIG. 11 . First, the AP determines theCFP (step S1101). For example, based on whether the STA-C is caused totransmit the uplink signal in one of the period from the time t0 to thetime t1 and the period from the time t2 to the time t3, the AP candetermine one of the period until the time t2 and the period until thetime t4 as the CFP. Note that, for example, the AP may determine theperiod until the time t4 as the CFP regardless of a timing at which theSTA-C should perform communication. In this case, the AP can determinethe CFP in accordance with the determination of the time t4 made whenthe TWT IE is set. Subsequently, the AP notifies the STA-C (andsurrounding wireless terminals) of the CFP (step S1102) by, for example,the Beacon 407. Subsequently, in accordance with a shift to a period inwhich the STA-C should communicate (YES in step S1103), the AP transmitsa polling frame to the STA-C (step S1104) and receives an uplink signalfrom the STA-C (step S1105). Then, the AP transmits an acknowledge tothe uplink signal (step S1106) and terminates the process.

Thus, in this processing example, the AP can control the communicationperiod of the STA-C by using the pulling frame. This makes it possibleto prevent the signal transmitted from the STA-C from interfering withthe signal (for example, the Trigger frame 413) regarding communicationbetween the AP, and the STA-A and the STA-B. Note that the AP canconfirm whether the STA-C supports polling (CF-Poll or QoS CF-Poll) byexchanging capability information at the time of connection with theSTA-C. This allows the AP to use a method in this processing exampleonly if the STA-C supports polling. Note that if the STA-C does notsupport polling, the AP can communicate with the STA-C by using, forexample, the method in processing example 1, the method in processingexample 2, or the like. That is, in accordance with the capabilityinformation of the STA-C, the AP can change the type of signal to betransmitted to set the communicable period of the STA-C appropriately.

As described above, the AP communicates with the first wireless terminalcapable of shifting to the sleep state in accordance with a schedule by,for example, the TWT of the IEEE802.11ax and the second wirelessterminal incapable of operating in accordance with the schedule whileadjusting a communication period. The AP transmits, to the secondwireless terminal, a predetermined signal for causing the secondwireless terminal not to perform communication in the first period inwhich the first wireless terminal is not in the sleep state or forcausing the second wireless terminal to perform communication in thesecond period in which the first wireless terminal is in the sleepstate. This predetermined signal can be, for example, a CTS-to-selfframe configured to set the first period to a NAV period or a PSMP framethat determines the second period as a communication period.Alternatively, the predetermined signal may be a combination of a signalsuch as a Beacon indicating that a period including the first period isset as the CFP and a polling frame transmitted to the second wirelessterminal in the second period during the CFP. This allows the secondwireless terminal to perform communication in the first period, makingit possible to prevent an interference with communication between thefirst wireless terminal and the AP. Note that a plurality of firstwireless terminals may exist, and the first period (including, forexample, transmission of a control signal from the AP) can be a periodin which multiuser communication in an uplink is to be performed. Inthis case, with the above-described method, it becomes possible toreduce the probability of occurrence of an interference that mayinfluence a plurality of wireless terminals at once.

According to the present invention, it is possible to set an appropriatecommunicable period in accordance with the characteristics of a terminalapparatus.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-085613, filed Apr. 24, 2017, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A communication apparatus functioning as anaccess point comprising: one or more memories having instructions storedtherein; and one or more processors that, upon execution of theinstructions, is configured to: perform, with a first othercommunication apparatus that can operate in accordance with firstinformation that is related to Target Wake Time (TWT) and that isschedule information for putting another communication apparatus into acommunicable state, communication based on the first information,wherein the first other communication apparatus is included in a networkformed by the communication apparatus; and set, in a case where a secondother communication apparatus that cannot operate in accordance with thefirst information is included in the network formed by the communicationapparatus, a Network Allocation Vector (NAV) for the second othercommunication apparatus, wherein the NAV is set for the second othercommunication apparatus while the first other communication apparatus isin a Doze state.
 2. The apparatus according to claim 1, wherein thefirst information is a TWT IE, Information Element.
 3. The apparatusaccording to claim 1, wherein the one or more processors is, uponexecution of the instructions, further configured to transmit a CTS,Clear To Send, to self frame for setting the NAV for the second othercommunication apparatus.
 4. The apparatus according to claim 1, whereinthe communication apparatus complies with an IEEE802.11 standard series.5. The apparatus according to claim 1, wherein the first informationcontains information of a timing to transit to the communicable state.6. The apparatus according to claim 1, wherein the communicable state isan Awake state in an IEEE802.11 standard series.
 7. The apparatusaccording to claim 1, wherein the first other communication apparatuscomplies with the IEEE802.11ax standard.
 8. The apparatus according toclaim 1, wherein the NAV is set for the second other communicationapparatus under a condition that the second other communicationapparatus that cannot operate in accordance with the first informationis included in the network formed by the communication apparatus.
 9. Theapparatus according to claim 1, wherein the one or more processors is,upon execution of the instructions, further configured to: receive a TWTrequest from the first other communication apparatus; transmit a TWTresponse to the first other communication apparatus, the TWT responseincluding information indicating listen interval; and transmit aplurality of beacons; wherein the plurality of beacons include a firsttype of beacon that is periodically transmitted based on the listeninterval and that contains a TWT IE, Information Element, and a secondtype of beacon that is not periodically transmitted based on the listeninterval and that does not contain the TWT IE.
 10. The apparatusaccording to claim 1, wherein the one or more processors is, uponexecution of the instructions, further configured to: in a case wherethe network formed by the communication apparatus includes an apparatusthat can operate in accordance with the first information and anapparatus that cannot operate in accordance with the first information,transmit a beacon including the TWT IE, and transmit information forsetting a NAV for another apparatus included in the network.
 11. Theapparatus according to claim 1, wherein the one or more processors is,upon execution of the instructions, further configured to: transmit abeacon including the TWT IE; and determine a duration of a NAV based onscheduling information defined by the TWT IE, wherein the NAV with thedetermined duration is set for the second other communication apparatus.12. A method for controlling a communication apparatus functioning as anaccess point, the method comprising: performing, with a first othercommunication apparatus that can operate in accordance with firstinformation that is related to Target Wake Time (TWT) and that isschedule information for putting another communication apparatus into acommunicable state, communication based on the first information,wherein the first other communication apparatus is included in a networkformed by the communication apparatus; and setting, in a case where asecond other communication apparatus that cannot operate in accordancewith the first information is included in the network formed by thecommunication apparatus, a Network Allocation Vector (NAV) for thesecond other communication apparatus, wherein the NAV is set for thesecond other communication apparatus while the first other communicationapparatus is in a Doze state.
 13. A communication apparatus functioningas an access point comprising: one or more memories having instructionsstored therein; and one or more processors that, upon execution of theinstructions, is configured to: receive a TWT request from a first othercommunication apparatus; transmit a TWT response to the first othercommunication apparatus, the TWT response including informationindicating listen interval; and transmit a plurality of beacons, whereinthe plurality of beacons include a first type of beacon that isperiodically transmitted based on the listen interval and that containsa TWT IE, Information Element, and a second type of beacon that is notperiodically transmitted based on the listen interval and that does notcontain the TWT IE; perform, with the first other communicationapparatus that can operate in accordance with first information that isrelated to Target Wake Time (TWT) and that is schedule information forputting another communication apparatus into a communicable state,communication based on the first information, wherein the first othercommunication apparatus is included in a network formed by thecommunication apparatus; and set, in a case where a second othercommunication apparatus that cannot operate in accordance with the firstinformation is included in the network formed by the communicationapparatus, a Network Allocation Vector (NAV) for the second othercommunication apparatus.
 14. The apparatus according to claim 13,wherein the first information is a TWT IE, Information Element.
 15. Theapparatus according to claim 13, wherein the one or more processors is,upon execution of the instructions, further configured to transmit aCTS, Clear To Send, to self frame for setting the NAV for the secondother communication apparatus.
 16. The apparatus according to claim 13,wherein the communication apparatus complies with an IEEE802.11 standardseries.
 17. The apparatus according to claim 13, wherein the firstinformation contains information of a timing to transit to thecommunicable state.
 18. The apparatus according to claim 13, wherein thecommunicable state is an Awake state in an IEEE802.11 standard series.19. The apparatus according to claim 13, wherein the first othercommunication apparatus complies with the IEEE802.11ax standard.
 20. Amethod for controlling a communication apparatus functioning as anaccess point, the method comprising: receiving a TWT request from afirst other communication apparatus; transmitting a TWT response to thefirst other communication apparatus, the TWT response includinginformation indicating listen interval; and transmitting a plurality ofbeacons, wherein the plurality of beacons include a first type of beaconthat is periodically transmitted based on the listen interval and thatcontains a TWT IE, Information Element, and a second type of beacon thatis not periodically transmitted based on the listen interval and thatdoes not contain the TWT IE; performing, with the first othercommunication apparatus that can operate in accordance with firstinformation that is related to Target Wake Time (TWT) and that isschedule information for putting another communication apparatus into acommunicable state, communication based on the first information,wherein the first other communication apparatus is included in a networkformed by the communication apparatus; and setting, in a case where asecond other communication apparatus that cannot operate in accordancewith the first information is included in the network formed by thecommunication apparatus, a Network Allocation Vector (NAV) for thesecond other communication apparatus.